Jack is one of the most introverted chimeras in existence; he makes Elish seem like a social butterfly. The Grim, as his family calls him, is quiet, reserved, and prefers only the company of his devoted sengil/cicaro Juni and his black cat Jett the 7th. He only leaves his skyscraper for family gatherings or when he has to work. Jack's job in the family is the Grim Reaper; he collects the remains of immortal and mortal chimeras and brings them back to his tower. If they are mortal he cremates them and gives the remains to Silas for a funeral. For the immortal chimeras, Jack washes their bodies, trims their hair and fingernails, shaves them, and if necessary re-circumcises them (if done early into resurrection the wound will quickly heal as their body is being repaired). He then wraps them in silks and lays them on daybeds he has in his library. Jack enjoys his job because, as he says 'the dead do not speak' and he does hate the company of other people.

Jack wasn't always this way though. When he was younger, though still introverted and shy, Jack was a happy chimera who was quite involved with his family. When Sanguine broke up with him to become Silas's sengil he retreated into himself and shut himself up in his and Sanguine's skyscraper. He became incredibly isolated to the worry of the family and extremely depressed, to the point where he would purposely kill himself in gruesome ways to keep himself dead for long periods of time. The person that brought him out of this depression was none other than Elish, who started spending time with Jack, even if it was just sitting with him in silence. Slowly Jack crawled out of his depression and even had a brief but intense relationship with Elish, though they decided, mutually, they were better off remaining brothers. The two still have pull with each other though, and Elish has used his power over Jack if he is in need of a favour. Even if their relationship didn't last, Elish had a good influence on Jack and his guidance is what pulled Jack out of his depression, and though still moros, Jack no longer wishes for death. He has even had several relationships after Sanguine and Elish, though he is currently single (to Juni's happiness though he keeps that to himself).

Jack is a gifted artist and is always being inspired to paint new things. He has painted many portraits of his brothers, ones which are hung with pride around the skyscrapers and in the pre-Fallocaust museum as well. Jack is also a talented singer and musician and enjoys singing with his sengil Juni, though only when no one else is around. Jack also loves vintage furniture, furniture that was old even before the Fallocaust, and vintage paintings as well. He also dresses in a unique way, wearing everything from surcoats to netted gloves, cowboy boots to cloaks. He also has no problem wearing makeup and will most often be seen in black eyeliner and black lipstick.

Jack lives in his skyscraper, Black Tower, with his immortal sengil/cicaro Juni Dekker, and his cat Jett the 7th.